The instant invention relates to the preparation of alkylhalodisilanes from phenyl-containing disilanes. More specifically, the instant invention relates to the preparation of alkylhalodisilanes having the formula, EQU R.sub.3-a X.sub.a SiSiR.sub.3-b X.sub.b,
wherein each R is an independently selected alkyl group; X is a halogen atom; a has a value of 0, 1, 2, or 3; and b has a value of 1, 2, or 3.
Alkylhalodisilanes have value as chemical intermediates. Nagai et al., Org Pre. Proc. Intl., 13. pg 118 (1981), discloses the synthesis of p-bis(hydroxydimethylsilyl)benzene starting with the reaction of 1,2-dichloro-1,1,2,2- tetramethyldisilane and p-dibromobenzene. Matsumoto, J. Synth. Org. Chem. Japan, 40, pp. 490-500 (1982), discloses the preparation of allylmethyldichlorosilane from the reaction of 1,1,2,2-tetrachloro-1,2-dimethyldisilane with allyl chloride.
The alkylhalodisilane, (CH.sub.3).sub.3 SiSiCH.sub.3 Cl.sub.2, has been shown to be a useful monomer in the preparation of polysilane polymers. Ziegler et al., Polymer Preprints, 28 (1). pp. 424-425 (1987), shows that polysilane polymers prepared from this monomer have unique photochemical properties.
Methylchlorodisilanes are a by-product of the preparation of methylchlorosilanes via the direct process reaction of methyl chloride with silicon. The by-product methylchlorodisilanes will be a mixture of all possible combinations methyl-containing and chlorine-containing disilanes. Extensive distillation would be necessary to isolate the desired disilane species.
Bettler et al., Inorganic Chemistry, 9(5), pp. 1060-1065 (1970), discloses the preparation of 1,1,1,2-tetramethyldichlorodisilane via the reaction of bis(trimethylsilyl)mercury with methyldichlorosilane. Hexamethyldisilane was a by-product of this reaction.
Kumada, Ishikawa, and Maeda, J. Organometallic Chem., 2, pp. 478-484 (1964), disclose that certain alkylhalotrisilanes and alkylhalotetrasilanes can be prepared from the corresponding phenyl-substituted alkylpolysilanes by reaction with hydrogen chloride in chloroform solvent in the presence of anhydrous aluminum chloride. However, Kumada et al. discloses that this chlorodephenylation reaction is only applicable to phenyl-substituted methylchloropolysilane where a silicon atom is attached to only one phenyl grup. In the examples of Kumada et al., reaction times of about 16 hours and moderate yields ranging from 53 to 76 percent are disclosed.
Kumada et al. J. Organometallic Chem., 43(2); pp. 293-305 (1972), discloses two methods for preparing 1,1-dichlorotetramethyldisilane from 1,1-diphenyltetramethyldisilane. In the first method, 1,1-diphenyltetramethyldisilane was added to cold concentrated sulfuric acid. Ammonium chloride was then added to the acid mixture. The resulting organic layer was separated and distilled. A yield of 61 percent 1,1-dichlorotetramethyldisilane resulted.
In the second method disclosed by Kumada et al. aluminum chloride was added to a benzene solution of 1,1-diphenyltetramethyldisilane. Dry hydrogen chloride was passed through the solution. The resulting mixture was distilled. A yield of 69 percent 1,1-dichlorotetramethyldisilane resulted.
Ishikawa et al., J. Organometallic Chem., 118(2), pp. 139-153 (1976), discloses a similar preparation of 1,1-dichlorotetramethyldisilane as reported by Kumada et al. in which anhydrous aluminum chloride is added to a benzene solution of 1,1-diphenyltetramethyldisilane, this mixture then being contacted with dry hydrogen chloride. The result was a 59 percent yield of 1,1-dichlorotetramethyldisilane.
Hengge et al., Monatsh. Chem., 106(4); pp. 887-892 (1975), discloses the preparation of several methylhalodisilanes from phenyl-containing disilanes. One of the materials disclosed was the preparation of 1,1-dichloro-1,2,2,2-tetramethyldisilane from 1,1,1,2-tetramethyl-2,2-diphenyldisilane. The 1,1,1,2-tetramethyl-2,2-diphenyldisilane was placed in a sealed tube with excess hydrogen chloride gas. The contents of the sealed tube were held for 5 days. The liquid was then distilled to give a 94 percent yield of 1,1-dichloro-1,2,2,2-tetramethyldisilane. Hengge et al. does not mention the use of any catalyst to facilitate the reaction.